Today's designs used for dust collection are based on various methods.
1. Cyclones extract dust from air or gas by centrifuging the mixture of air and dust or gas and dust in cone shaped vertical receivers. Due to centrifugal action the heavy particles of dust and soot impinge on the inside wall of the cone gradually progressing by weight to the bottom of the cone into a collecting receptacle.
2. Dust-extracting boxes through which air or gas carrying dust flows along the walls of dust-adsorbing material forming labyrinths. Dust clings to the walls and the accumulated dust layers becoming heavy separate from the walls falling into collecting troughs.
3. Dust-arresting sieves in frames enclosed within cameras through which dust-laden air or gas flows leaving behind layers of dust clinging to the sieves. These sieves are periodically cleaned.
4. Air or gas washing compartments also called scrubbers. Water sheet or water spray in the compartments impinge on the dust and soot particles and the resulting slush falls into collecting troughs. The washing by water cools the gas or air and as a result slows down the draught and consequently the velocity of gas flow to the stack and out of the stack above the vicinity.
5. Electric precipitators in dust collecting cameras charge dust particles with an electric charge. The charged particles are attracted by the electrodes. The accumulated dust on the electrodes is periodically removed.
All these designs are bulky and expensive. They all require periodic removal of contaminants accumulated in the collectors. The removal requires the shut-down of the gas or air flow. Alternatively double collectors are fitted. One of the collectors is in use whilst the other is being cleaned.
None of these collectors entirely remove the dust and soot particles from the air or gas flow. These residual unremoved particles within the air or gas flow are carried high up in the stack. The air or gas gradually descends to the ground level carrying with it the residual dust and soot particles causing pollution of the vicinity. This is the case when there is no wind around the stack. When there is a wind the contaminants are carried in the direction of the wind, and depending upon the velocity of the wind cause pollution in areas close to the stack or far away from it.
The present invention removes these contaminants at the exit from the stack just before the gas or air carrying the contaminants enter the atmosphere.
There might be cases when gas only with no contaminants emanates from the stack. The gas might be as a result of a chemical process and has a harmful effect on human beings even when mixed with air around the area of the stack or when carried far away from the stack by the wind. Sprays of water into the gas according to this invention may wash the gas and lessen the harmful effect. The invention can be used as a second and final stage of removal of the contaminants left over from the dust collectors installed before the gas or air enter the stack.
Alternatively the invented dust collector will remove all contaminants at the exit from the stack when due to lesser density of contamination previous stages of dust collecting are not necessary, thereby saving on investment.
Today's stacks disperse contaminants left in the gas or air flowing from the dust collectors, high above the ground to improve ecology. This invention will make the construction of high stacks unnecessary in most cases. These contaminants are extracted entirely at the stack exit as further described and are not dispersed into the surrounding air.